In my experience it is not enough to disable third party Antivirus - it has to be completely uninstalled. At least one major AV (can't remember which) still leaves its TCP/IP hooks in the kernel even when disabled making network traffic several times slower. Customers are aghast at the suggestion that AV is the problem - surely you are the one with the bad code. They think AV couldn't possibly slow all disk and net accesses by an order of magnitude.